In communication system, scheduling algorithms uses two kinds of measurement information, i.e., channel status information and traffic measurement information (quantity and priority) for scheduling. Such information is obtained using feedback through a signaling channel, direct measurement in a base station (eNodeB: Evolved NodeB), or both. The quantity of feedback is an importantly considered element. The channel status information and the traffic information helps increase scheduling efficiency, but takes high overhead cost. Such trade-off is common to all systems using a feedback-based resource scheduling scheme.
Generally, in the case of downlink scheduling, buffer information may directly be obtained from a base station (eNodeB), and channel information may be obtained through a Channel Quality Indicator (CQI) that is used for an adaptive modulation and coding scheme. On the other hand, in the case of uplink scheduling, channel information may be obtained through a packet that is directly received from a base station (eNodeB), and buffer information may be obtained through Buffer Status Reporting (BSR) feedback from User Equipment (UE).
3GPP-LTE provides a BSR scheme for uplink scheduling. The BSR scheme may largely divided into regular BSR, periodic BSR and padding BSR. Whether these BSR schemes are performed is determined through a timer that is set in Radio Resource Control (RRC) or a trigger that is started by a specific event, and detailed content is as follows.
For regular BSR and periodic BSR:
In Transmit Time Interval (TTI) where BSR is transmitted, long BSR is reported when one or more Logical Channel Groups (LCG) have data usable for transmission.
Otherwise, short BSR is reported.
For padding BSR:
When the number of padding bits is equal to or larger than the size that is obtained by adding a sub-header to short BSR or is less than the size that is obtained by adding a sub-header to long BSR
In TTI where BSR is transmitted, when one or more LCG have data usable for transmission, the truncated BSR of an LCG having a logic channel of the highest priority that has transmittable data is reported.
Otherwise, short BSR is reported.
When the number of padding bits is equal to or larger than magnitude that is obtained by adding a sub-header to long BSR, long BSR is reported.
In BSR Medium Access Control (MAC) elements, the associated with BSR is configured with the following elements.                Short BSR and truncated BSR format: one buffer size field related to one LCG ID field        Long BSR format: LCG ID #0 to #3 associated with four buffer size fields        
BSR format is checked through a MAC Packet Data Unit (PDU) sub-head having LCID. LCG ID and buffer size are defined as follows.                LCG ID: this is used to check a logic channel group in which a buffer status is reported with a logic channel group ID field. The length of the field is 2 bits.        Buffer size: a buffer size field is used to check the total amount of data usable through all the logic channels of a logic channel group after an MAC PDU is generated. The amount of data is indicated in byte units. A Radio Link Control (RLC) layer and a Packet Data Convergence Protocol (PDCP) layer include all data usable for transmission. The size of an RLC header and the size of an MAC header are not included in the calculating of buffer size. The length of this field is 6 bits.        
In FIGS. 1 and 2, the type of a BSR format is illustrated. FIG. 1 illustrates a short or truncated BSR format. FIG. 2 illustrates a long BSR format.
The above-described buffer status reporting method of 3GPP LTE is made on the assumption of the short round-trip delay of a terrestrial communication system. On the other hand, in a satellite communication system, because buffer status information from UE is transferred from a satellite base station after a very long round-trip delay, there are limitations caused by the long round-trip delay. For example, since very long time is taken until a base station receives BSR relative to the terrestrial communication system, it is difficult to predict the change of a terminal buffer that occurs for the long time. That is, a base station cannot determine whether current-received BSR information is the one that data scheduled to be transmitted are reflected or not.
Moreover, since a satellite communication system having a long round-trip delay consequently performs uplink scheduling on the basis of the past buffer status information of a terminal, scheduling may not be performed in spite of much data to be transmitted, or scheduling may be performed even when there is no data to be transmitted.
There is a method proposed for decreasing the number of BSR times, in a terrestrial communication system. In this method, a base station predicts the buffer status estimation value of a terminal, compares the predicted value with an actual buffer status, and performs BSR only when the predicted value exceeds a certain critical value, thereby decreasing the number of BSR times. Since the base station predicts the buffer status of the terminal until a next buffer status is reported on the basis of initial buffer status information, it may less be affected by a long round-trip delay.
However, there is possibility that limitations may occur when the method is directly applied to the satellite communication system. If the buffer status estimation value of a terminal in a base station is expressed as Equation (1) below at arbitrary time ‘t0’, the actual buffer status of the terminal after Round Trip Time (RTT)/2 is expressed as Equation (2) below.B(t0)=B0−RA  (1)B(t0+½*RTT)=B0−RA+Bn  (2)where B0 is the initial buffer status of a terminal, RA is a capacity which a base station allocates to the terminal through scheduling at time ‘t0’, and Bn is the amount of data that is newly generated and is added to a buffer.
At this point, when the terminal informs the base station of the buffer status “B(t0+½*RTT)”, there is a strong possibility that the actual buffer status of the terminal may be different from a reported value when the base station of the satellite communication system receives the message, unlike the terrestrial communication system.
This is because there is a possibility that a satellite base station additionally allocates RA′ to a terminal or new Bn′ is additionally added to the terminal for time “½*RTT” when buffer status information is transmitted from the terminal to the satellite base station. If the terminal transmits BSR each time the amount of a buffer decreases by RA, the base station may calculate the additionally-decreased amount of the buffer on the basis of a value that is reported and an amount that is allocated to the terminal during the transmitting of BSR, but there is limitation that the amount of data that is newly added to the buffer for time “½*RTT” may not be reflected. Moreover, since the terminal does not transmit BSR each time the amount of the buffer decreases by RA but BSR is actually made through various reference triggers, a timer or padding, it is difficult for the base station to predict the accurate buffer status of the terminal on the basis of buffer status information that is reported in this way.
For example, when a satellite base station derives the buffer status of a terminal by using only buffer status information that is reported (i.e., the buffer status of the terminal that is decreased through scheduling in the base station is not derived), because the reporting of buffer status information increases or is identically maintained for a certain time although the amount of buffer of the terminal decreases through scheduling due to the long round-trip delay time of a satellite, scheduling may be performed even if there is no data to be transmitted. On the other hand, although the amount of the buffer increases newly, when the reporting of buffer status information is continuously made for a certain time during a preceding buffer status decreases, the reporting of buffer status information may be excluded from scheduling even though transmission should be started through scheduling.